1. Field of the Invention
This invention relates to solids handling, and more particularly to methods for introducing particulate solids into the bottom of a solids upflow vessel, such as a vertical solids upflow retort used for heat treating oil-producing or oil-containing solids to recover oil and/or gas therefrom.
2. Description of the Prior Art
The problem of transporting particulate solids from a solids feed supply, such as a bin or reservoir of the particulate solids, into the bottom of a solids upflow vessel has been encountered in diverse operations, exemplary of which are the feeding of oil-producing and/or gas-producing solids, such as oil shale, tar sand, bituminous coal, oil-saturated diatomaceous earth, and the like into the bottom of a vertical solids upflow retort for treating the solids to recover oil and/or gas therefrom, and the production of synthesis gas by the reaction of gas containing steam with carbonaceous solids such as coal, coke, and the like.
In these operations, difficulties are encountered in the design and operation of mechanical feed systems because of the nature of the particulate solids being transported, typical solids being abrasive and difficult to handle on the one hand and on the other being friable and tending to abrade, thereby forming large quantities of undesirable fine particles. Feeder devices used to introduce solids into the bottom of an upflow solids bed must move the solids against the weight of the solids bed. Also, it is often the case that the solids must be transported from a storage bin at atmospheric pressure into a solids upflow vessel which operates at a superatmospheric pressure. These factors, coupled with the often gigantic size of the equipment required to obtain the desired solids handling capacity, and the fact that in some applications the feeder device must operate at elevated temperatures and in contact with liquids and/or gases produced in the solids treating process, present difficult design problems involving large and complex mechanical forces and complicated mechanical loadings that must be adequately provided for in the feeder design.
A number of different methods for introducing particulate solids into the bottom of a solids upflow vessel have been proposed, including the methods disclosed in U.S. Pat. Nos. 2,501,153 to Berg, 2,640,014 to Berg, 2,871,170 to Bewley et al., 2,875,137 to Lieffers et al., 2,895,884 to Switzer, 4,033,467 to Bewley et al. and 4,037,736 to Pownall et al. In each of the methods disclosed therein a piston adapted for reciprocation within a feed cylinder is alternately extended to introduce particulate solids from the feed cylinder into the bottom of the solids upflow vessel and retracted to receive additional solids from a feed reservoir into the feed cylinder. The solids can be introduced into a stationary feed cylinder by horizontally reciprocatable scoops while slide plates prevent backflow of the charged solids (U.S. Pat. No. 2,871,170 to Bewley et al.) or the feed cylinder can be oscillated, reciprocated or rotated into alignment with a bottom solids outlet of the feed reservoir to receive additional solids therefrom while a seal plate mounted on the feeder mechanism prevents backflow of the charged solids.
One limitation of the prior art methods for feeding solids into a solids upflow vessel is that the very high feed piston-to-solids pressures generated during the feeder charging stroke results in relatively large power consumption by the feeder mechanism. In the prior art methods these high piston-to-solids pressures are present even after the feeder piston has been fully extended, and these high pressures are also exerted against the seal plate or slide plates used to prevent backflow of solids as the feed cylinder is being refilled. Moreover, these high pressures must be overcome in order to close the slide plates or to oscillate, reciprocate or rotate the feed cylinder into alignment with the feed reservoir during the feeder cycle. Another problem is that these high pressures require the use of relatively thick and therefore expensive seal plates or slide plates, the weight of which in turn necessarily increases the power consumption of the feeder mechanism during the feeder cycle. The use of thick slide plates may additionally result in process operating problems in a solids upflow vessel, such as an oil shale retort, due to the significant rise and fall of the solids bed as the slide plates are opened and closed, respectively. Moreover, the high piston-to-solids pressures of the prior art methods can result in the crushing of the particulate solids thereby generating a significant amount of fine particles which increase the fluid pressure drop across an oil shale retort and necessitate the use of more power to circulate the eduction gas through the retort. Thus, a need exists for an improved method for introducing particulate solids into the bottom of a solids upflow vessel.
Accordingly, a primary object of this invention is to provide an improved method for introducing solids upwardly into the bottom of a solids upflow vessel wherein the aforementioned problems are substantially reduced.
Another object of this invention is to provide a solids feeding method in which the maximum feed piston-to-solids pressure is reduced as compared to prior art methods.
Still another object of this invention is to provide a solids feeding method in which the power requirements are substantially reduced as compared to the prior art methods.
Yet another object of this invention is to provide a solids feeding method which allows the use of a lighter weight, less expensive apparatus to feed and support the bed of solids in the solids upflow vessel.
A further object of this invention is to provide an improved solids feeding method to which the prior art solids feeding apparatus can be readily and inexpensively adapted.
Still further objects, advantages and features of the invention will become apparent to those skilled in the art from the following description when taken in conjunction with the accompanying drawings.